With the increasing distances over which data is conveyed in present day communication systems, the need for equipment which maximizes the integrity of the data and minimizes or overcomes the effects of signal degradation and noise is of paramount importance. To achieve these functions communication systems usually employ signal regeneration circuitry at one or more locations along the communication link, typically in repearer stations that are used to couple remote transmitting and receiving stations with each other.
One type of signal regeneration circuit that has been proposed for use in a fiber optic communication environment is described in the U.S. Pat. No. 4,019,048 to Maione et al. In the regenerator described in that patent, signal timing recovery circuitry contains a wide range acquisition configuration made up of the combination of a frequency-lock loop and a phase-lock loop which purportedly is less expensive than what the patentees refer to as narrow range acquisition circuitry requiring expensive crystal control. The data rate for which the Maione et al circuit is used is what is termed in the art as T-3 data (on the order of 44 Mb/s), there being no consideration to the requirements of significantly higher data rates, such as T-4 data rates (on the order of 300 Mb/s).
In copending patent application Ser. No. 149,291, filed May 12, 1980, entitled Repeatered, Multi-Channel, Fiber Optic Communication Network having Fault Isolation System, by P. Casper et al, and assigned to the assignee of the present application, there is described a fiber optic communication system over which high data rate optically encoded digital signals are transmitted, wherein the system signal regeneration is carried out at repeater stations and within transceiver units that interface digitized telephone data traffic with the fiber optic links. The network described in this copending application is capable of transmitting what is termed in the art as T-4 data (on the order of 274-300 Mb/s), so that accurate and precise regeneration and timing of data is of significant importance, in order to provide as high a fidelity as possible output signal to users of the network and to permit accurate multiplexing and demultiplexing of the data signals, the control of which is highly dependent upon the relative timing of the signals involved. Now, while the signal regeneration circuit of the type described in the Maione et al patent may be suitable for T-3 data rates, to date there has not been developed a signal regeneration and timing circuit, to be described in detail below, which carries out the intended timing or synchronization functions for the much higher T-4 data rate signals in a fiber optic environment.